Cementitious materials can include various different types of cements, compounds, mortars, joint compounds, construction adhesives, and the like. These products typically contain a binder and a filler. The binder may comprise, for instance, a cement such as Portland cement or gypsum. The filler, on the other hand, may comprise a quartz sand or calcium carbonate.
In addition to a binder and a filler, the compositions can also contain various other additives. For instance, cellulose derivatives and other materials have been added to the cementitious compositions. The cellulose derivatives are added in order to improve the workability of the composition, to increase the water-retention properties of the composition, and to increase the adhesiveness and the resistance to sliding. Increasing water retention, for instance, can prevent the composition from losing water prior to setting on highly absorbent substrates and allows for control of the open time and adjusting time. If the composition sets too quickly, the resulting composite may not develop the mechanical adhesion strength required to keep a tile adhesive attached on the adjacent surface as well as to prevent cracks, for example. Workability is also improved due to the lubricant properties of the cellulose ethers. Cellulose derivatives may be used with or without a polyvinyl alcohol resin in cementitious tile adhesive compositions; see Great Britain 1,490,783 of Griffith et al. and Great Britain 1,225,755 of Vaughn et al., the disclosures of which are incorporated herein by reference. Latex and other resinous additives for cementitious compositions are also seen in the following references: European Patent Application Publication 0 649 823 which discloses the use of polyvinyl alcohol and polyvinyl acetate; U.S. Pat. No. 7,294,194 to Reddy et al. which discloses various latexes for preserving elasticity; and United States Patent Application Publication No. 2001/0018881 of Futami et al. which advocates the use of melamine and sulfonic acid/formaldehyde condensates, naphthalene sulfonic acid condensates and amide resins in cement.
Synthetic polymer additives for mortars are frequently supplied as redispersible powders or emulsions. The redispersible polymer may comprise, for instance, an emulsion made out of polyvinyl acetate homopolymer and copolymers stabilized with polyvinyl alcohol. The redispersible polymer may improve workability, sag resistance, flexibility and tension strength under standard conditions, but also after water immersion, heat aging and freeze-thaw cycles and so forth. Exemplary redispersible powders are described in European Patent Application Publication No. 1 158 007 of Hara et al. and European Patent Application Publication No. 0 873 978 of Hornamen et al., both of which relate to polyvinyl alcohol (PVOH) stabilized latexes. The disclosures of EP 1 158 007 and EP 0 873 978 are incorporated herein by reference.
Although the incorporation of cellulose derivatives, redispersible polymers and other additives has provided many advances in the art, some deficiencies still remain. For example, cellulose ethers when present in the composition can cause a considerable delay in cement setting. Redispersible polymers, on the other hand, can be relatively expensive, thus adding cost to the final product.
In view of the above, a need currently exists for additives that can further improve the properties of a cementitious composition. In particular, a need exists for additives that can be used to control the wet properties and the mechanical properties of a cementitious composition containing the additives. A need also exists for additives that can reduce or eliminate the amount of redispersible polymers in a cementitious composition without adversely affecting the properties of the composition. This need is based on both the high cost of redispersible powders, and the fact that high levels of redispersible powders can cause an imbalance in a cementitious composition. For example, redispersible powders can help impart flexibility; however they typically can hinder properties like water resistance.